Properties of Carbon-Supported Platinum Catalysts: Role of Carbon Surface Sites

The effect of oxidation treatments of the support on the properties of carbon-supported platinum catalysts has been analyzed. A set of activated carbon carriers has been prepared by oxidative treatments of a commercial carbon in liquid as well as in gas phase. The carbons obtained had largely identical pore structures but differed considerably in their surface chemistry as shown, for example, by their point of zero charge (PZC) values. The catalysts were prepared by equilibrium impregnation of the supports with an aqueous solution of hexachloroplatinic acid. N2 adsorption, TPD, XPS, TPR, and H2 chemisorption were used to characterize the supports and the catalysts. The Pt load of the catalysts was found to depend on the PZC of the supports. However, the Pt dispersion was found to depend on the total surface oxygen content of the supports. These results were rationalized by the assumption that the surface basic groups of the supports are anchoring sites for the strong adsorption of platinum.